This invention relates to a foundation for cellarless houses of the type comprising a suitably frame-like or otherwise endless foundation wall whose underside is disposed on a level below the surface of the ground surrounding the house and which serves to support the house while defining, together with a bearing floor structure, a bottom space in the area above the ground on which the house is erected, said floor structure having a lower portion which is air permeable in order, via said floor structure, to permit supplying air of substantially room temperature, suitably in the form of exhaust air from the interior of the house, to said bottom space from which the air is evacuated, suitably through an evacuation conduit or duct passing through the floor structure.
Cellarless houses have long been erected on foundations of basically two different types, via. either conventional cottage foundations with foundation walls of a considerable height or whole slabs placed directly on the ground.
Both conventional cottage foundation and foundation slabs are relatively expensive solutions to the foundation problem and, even in the most elaborate designs, do not provide for good heat comfort indoors. Also where the floors are rigorously insulated, they will never feel properly heated. For this and many other reasons, a novel type of foundation has lately been developed which may be referred to as forced flow foundation and which is based on the idea of conducting the relatively warm exhaust air from the interior of the house down into the space below the floor and from there through an air-permeable layer (which may consist of either the lower portion of the floor structure or a separate layer, e.g. of mineral wool, underneath the bearing floor structure) to the crawl way or bottom space from which the air is evacuated through a duct which extends up through the floor structure and the house and communicates with the ambient atmosphere. Such a forced flow foundation is disclosed in Swedish patent specification No. 7511197-1. The advantages of such a system are that it provides for good heat comfort in the form of warm floors in the house while minimising the amount of heat insulating material in the floor structure and, hence, heat insulation costs, and also that the depth of the foundation can be significantly reduced in that the space underneath the house is kept warm and will thus heat the ground below the house whereby to avoid frost heave.
However, since the forced flow system uses an insulated floor structure over a space defined by the foundation wall, it has hitherto been regarded merely as a further development of the conventional cottage type foundation. Thus, the underside of the floor structure has been disposed on a level above the ground surrounding the house with a high crawl way below the house and with the same, relatively complicated wall connections as in the conventional cottage type foundation. As opposed to the relatively poor and inexpensive insulation of the upper portion of the foundation wall used in the cottage type system, the foundation wall of the forced flow system must however be insulated in its entirety both accurately (in a moisture-proof way) and extensively, since heat losses through the foundation wall are not acceptable. The savings of the forced flow system by a reduced foundation depth and less insulation of the floor structure have therefore been offset by the increased insulation of the foundation wall and the more expensive mounting of the so-called pressure drop or distributing layer which is required for allowing air to pass between the interior of the floor structure and the underlying crawl way. In view hereof, the forced flow system, despite its advantages in respect of insulation and heat comfort, has not had any notable commercial success.